Long-Term Surveillance of Avian Coronaviruses from Wild Bird in South Korea

We examined 2,868 fecal samples from migratory wild birds collected from multiple geographical locations in South Korea during the winter seasons between 2014 and 2022. All samples were obtained from four avian species belonging to the genus Anas within the order Anseriformes: Eurasian teal (Anas crecca), Eastern spot-billed duck (Anas zonorhyncha), Mallard (Anas platyrhynchos), and Northern pintail (Anas acuta). The presence of coronaviruses (CoVs) was confirmed through nested PCR targeting a conserved region of the RNA-dependent RNA polymerase (RdRp) gene. A total of 28 samples (0.97%) were tested positive for CoVs, comprising 17 Gamma coronaviruses (γ-CoVs) and 11 Delta coronaviruses (δ-CoVs). Sequence analysis of newly identified strains showed similarity ranging from 79.2% to 99.4% for γ-CoVs and from 72.5% to 100% for δ-CoVs, with an overall similarity of 74%. However, sequence homology between γ-CoVs and δ-CoVs was below 60%. The detected γ-CoVs belonged to two subgenera: Igacovirus (Duck-CoV 2714-like) and Brangacovirus. The δ-CoVs were classified under the Buldecovirus subgenus. Among them, seven detected strains were related to the representative porcine δ-CoV strain HKU15, while four strains clustered within subgroup 1 of Buldecovirus. Delta coronaviruses have been found in a variety of hosts, including humans and mammals, raising concerns about potential interspecies transmission. Evidence of genetic linkage between avian and porcine δ-CoVs was observed. Notably, recent reports indicate that three Haitian children were infected with porcine δ-CoVs. This study aimed to investigate the diversity of CoVs in avian species, and for the first time in South Korea, we report the detection of δ-CoVs in wild birds.